Compact multiple effect still having stacked
impervious and pervious membranes

ABSTRACT

THE COMPACT, MULTIPLE EFFECT STILL IS COMPOSED OF ALTERNATING LAYERS IN STACKED RELATIONSHIP OF THIN POROUS MEMBRANES THAT AREIMPERVIOUS TO LIQUIDS WHILE READILY PASSING THE VAPORS THEREOF AND CORRUGATED MEMBRANES THAT ARE IMPERVIOUS TO LIQUIDS AND VAPORS.

A ril 23, 1974 F. A. RODGERS 932 COMPACT MULTIPLE EFFECT STILL HAVINGSTACKED IMPERVIOUS AND PERVIQUS MEMBRANES Original Filed May 26, 1966 5Sheets-Sheet l A nl 23, 1974 F. A. RODGERS 982 COMPACT MULTIPLE EFFECTSTILL HAVlNu TACKED IMPERVIOUS AND PERVIOUS MEMBRANES Original Filed May26, 1966 5 Sheets-Sheet 2 April 23, 1974 F. A. RODGERS 27, 932

COMY ACT MULTIPLE EFFECT STILL HAVING STACKED IMPERVIOUS AND PERVIOUSMEMBRANES 1966 5 Sheets-Sheet 3 Original Filed May 26,

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COMPACT MULTIPLE EFFECT STILL HAVING STACKED IMPERVIOUS AND PERVIOUSMEMBRANES 196E 5 Sheets-Sheet 4 Original Filed May 26.

FIG?

April 23, 1974 RODGERS Re. 27, 982

COMPACT MULTIPLE EFFECT STILL HAVING STACKED IMPERVIOUS AND PERVIOUSMEMBRANES Original Filed May 26. L966 5 Sheets-Sheet 5 l 3 FIG. ll 7427,982 COMPACT MULTIPLE EFFECT STILL HAVING STACKED IMPERVIOUS ANDPERVIOUS MEMBRANES Franklin A. Rodgers, Brookline, Mass., assignor toPactide Corporation, Cambridge, Mass.

Original No. 3,497,423, dated Feb. 24, 1970, Ser. No. 553,190, May 26,1966, which is a continuation-in-part of application Ser. No. 510,014,Nov. 26, 1965, now Patent No. 3,406,096. Application for reissue Nov. 8,1971, Ser. No. 196,703

Int. Cl. B016 3/02; C02b 1/06 US. Cl. 202-174 8 Claims Matter enclosedin heavy brackets I: 1 appears in the original patent but forms no partof this reissue specification; matter printed in italics indicates theadditions made by reissue.

ABSTRACT OF THE DISCLOSURE The compact, multiple effect still iscomposed of alternating layers in stacked relationship of thin porousmembranes that are impervious to liquids while readily passing thevapors thereof and corrugated membranes that are impervious to liquidsand vapors.

This application is a continuation-in-part of copending U.S. applicationSer. No. 510,014, filed Nov. 26, 1965, now US. Patent No. 3,406,096.

This invention relates to novel and improved distillation apparatus fortransferring liquid directly from one body of liquid to another across avapor permeable barrier.

In the copending US. patent application of Franklin A. Rodgers, Ser. No.456,404, filed May 7, 1965, now abandoned, there is describeddistillation apparatus particularly adapted for the desalination ofwater and including as the basic components thereof, a porous membranethat operates as a barrier to liquids while readily passing the vaporsof the liquids, means for forming thin evaporating and condensing layers[or membranes] of the liquids in contact with opposite sides of theporous membrane, and means for transferring heat to the evaporatinglayer and from the condensing layer. The porous membrane includes amultiplicity of microscopic, gas-filled, through passages having wallsnon-wettable by the liquid for passing substantially only the vapor ofthe liquid and gases dissolved therein from the evaporating layer to thecondensing layer. The porous membrane and the means for forming theevaporating and condensing layers preferably constitute one liquidtransfer stage of a multiple stage still in which adjacent condensingand evaporating layers of adjacent stages are separated by liquid andvapor impermeable barriers, and heat is transferred from the condensinglayer of each stage to the evaporating layer of the next succeedingstage.

Objects of the invention are: to provide multiple stage distillationapparatus of the type described having a novel, improved and lessexpensive construction that facilitates fabrication and assembly of themultiple stage apparatus and provides for more etficient operation; andto provide, in multiple stage distillation apparatus as describedcomprising a plurality of porous and impermeable barrier membranessandwiched together, an improved barrier membrane configurationproviding [to] for improved liquid flow characteristics.

Other objects of the invention will in part be obvious and will in partappear hereinafter.

The invention accordingly comprises the apparatus possessing theconstruction, combination of elements and arrangement of parts which areexemplified in the follow- United States Patent ing detailed disclosure,and the scope of the application of which will be indicated in theclaims.

For a fuller understanding of the nature and objects of the invention,reference should be had to the following detailed description taken inconnection with the accompanying drawings wherein:

FIGURE 1 is a perspective view, partially in section, showingdistillation apparatus embodying the present invention, with thethickness of components exaggerated for purposes of illustration;

FIG. 2 is a fragmentary, exploded, perspective view of components of theapparatus of FIG. 1, shown with some of the dimensions, primarilythickness, exaggerated;

FIG. 3 is a sectional view of the apparatus of FIG. I, the section beingtaken lengthwise thereof;

FIG. 4 is a fragmentary plan view, partially in section, of a portion ofthe apparatus;

FIG. 5 is a fragmentary sectional view of components, includingmembranes, of the apparatus taken substantially along the line 5-5 ofFIG. 4;

FIG. 6 is an enlarged sectional view showing in detail the constructionof the apparatus;

FIG. 7 is an enlarged sectional view similar to FIG. 6, illustratingother components of the apparatus;

FIG. 8 is a fragmentary plan view similar to FIG. 4 illustrating theconstruction and operation of another embodiment of the apparatus;

FIG. 9 is a sectional view taken substantially along the line 9-9 ofFIG. 8;

FIG. 10 is a fragmentary perspective view showing another embodiment ofa component of the still; and

FIG. 11 is an enlarged, fragmentary sectional view of a portion of thestill embodying the membrane shown in FIG. 10.

The present invention is incorporated in an inexpensive yet highlyetlicient, compact, multiple effect still made possible largely by theprovision of thin porous membranes that are impervious to liquids whilereadily passing the vapors thereof. The basic components of the stillincluding a multiplicity of such porous membranes arranged in stackedcontiguous relation together with vapor and liquid impervious membranesdisposed between the porous membranes to separate the condensing layer(liquid) of each stage from the evaporating layer of the next succeedingstage. Both the porous and im previous membranes are quite thin as arethe liquid layers confined therebetween so that a large number ofdistillation stages can be embodied in a relatively small assembly, andthe membranes are preferably formed of materials, particularly organicplastics, that are inexpen sive and easy to fabricate.

As previously noted, the basic components of an individual distillationstage are a porous membrane and an imprevious membrane for forming andmaintaining the liquid evaporating and condensing layers. The porousmembrane is substantially as described in the aforementioned applicationand comprises a thin sheet material formed with a multiplicity ofmicroscopic through pores or passages of substantially uniform size, andoccupying the major portion (e.g. 85%) of the total volume of themembrane. The porous membrane is designed to permit operation of thestill with the films or layers of evaporating and condensing liquids indirect contact with the surfaces of the porous membrane and with theliquids at hydrostatic pressures equal to or greater than the pressuresof the other portions of the system, particularly the gas within thepores of the membrane. To make this operating condition possible whilereducing to a minimum the resistance to ditiusion of vapor, the poresare preferably of a maximum size while being so constituted as to beunable to pass the liquid, and the apparatus is operated underconditions such that the pores contain only the vapor of the liquid andany gas dissolved therein substantially at the vapor pressure of theliquid (and any dissolved gas).

Materials useful for the porous membrane include organic plastics thatare insoluble in and compatible with the particular vaporizable liquid(eg. water) to be purified by the distillation apparatus, and able towithstand the operating temperatures encountered. Materials useful forthe porous membrane in Stills designed to desalinate water, include, forexample, polyvinyl chloride, cellulose nitrate, cellulose acetate,cellulose triacetate, nylon, and polytetrafluoroethylene. The porousplastic membrane may be inherently non-wettable by the liquid and/or itmay be treated in such a way as to render the surfaces including thepores, non-wetting. For example, a cellulose nitrate microscopic porousfilter media, such as sold by Millipore Filter Corporation under thetrademark Standard MF and having a thickness of approximately 0.006 inchand pores with an effective diameter of 0.45 micron, may be coated witha silicone water repellant such as sold by General Electric Companyunder the trade name Dri-film" No. 1040 or No. 1042, or designated SS4029, to provide a non-wetting porous membrane suitable forincorporation in the still of the invention.

In a multiple effect or multiple stage still, liquid and vaporimpermeable barrier [membrances] membranes are alternated with porousmembranes to form, maintain and separate the evaporating and condensinglayers [of] or sheets of liquid as well as to provide a good thermalconduction for promoting heat-transfer from the condensing layer of eachstage to the evaporating layer of the next succeeding stage. Theimpermeable barrier membranes are formed of the thinnest possible sheetmaterial in order to reduce resistance to heat transfer to a minimum,particularly in stages of the apparatus at which the operatingtemperature is relatively low and thermal conductivity may constitute amajor factor in overall operating efliciency. The composition of theimpermeable barrier membrane depends primarily on the nature of theparticular liquids involved including compatibility of the membrane withthe liquids, the operating temperature of the apparatus, cost, ease offabrication and assembly, and thermal conductivity. Suitable materialsinclude metals such as copper and aluminum having good thermalconductivity and available in sheet form, and less expensive materials,particularly organic plastics, having the requisite structural strengthat the operating conditions of temperature and pressure. Sheet materialsparticularly suitable as impervious membranes useful in stills designedto desalinate water include fiuorocarbons such as polyvinylidenefluoride, and polycarbonates, desirable because of their superiordimensional and chemical stability under conditions of 100% humidity andhigh temperature and resistance to damage from biological growth.

The present invention is particularly concerned with the fabrication andassembly of the porous and impermeable membranes to form a compact,efiicient and inexpensive multiple effect still in which shallowpassages are provided between adjacent membranes for conducting andpermitting the free flow of liquids constituting the evaporating andcondensing layers [of] or sheets. Reference is now made to FIGS. 1through 3 of the drawings wherein there is illustrated a multiple effectstill embodying the invention. For purposes of clarity of illustration,many of the dimensions of the elements, particularly thickness, havebeen exaggerated or otherwise shown distorted out of proportion. Thestill comprises a multiplicity of [fiat] porous membranes and imperviousbarrier membranes 12 assembled together in alternating stackedcontiguous relation between a pair of header plates 14 and 16. Theporous and barrier membranes are preferably rectangular in shape andsubstantially coextensive with one another, and the header plates arelocated on opposite sides, i.e., top and bottom, of the stack of films,are also rectangular and extend beyond the edges of the stack ofmembranes. Header plates 14 and 16 function to retain the stack ofmembranes together as an assembly and are formed with through holes 18near the end and longitudinal edges to accommodate bolts 20 for clampingthe stack of membranes between the header plates under compressivepressure at the margins of the [films] stack. In an alternativeembodiment, the header plates may be constructed (e.g., in the form offrames) to apply compressive pressure only to the margins of the stacksand thereby perform their basic function of preventing escape of liquidsat the edges of the membranes.

In the form of still shown, the membranes and header plates aregenerally planar and although they still may be operated insubstantially any position or in a zero gravity environment, it ispreferably oriented with the membranes, header plates, and layers ofevaporating and condensing liquids disposed in horizontal planes. Theassembly comprises, in order, an upper header plate 14, an imperviousmembrane 12, a multiplicity of porous membrane 10 arranged inalternating, repetitive order, and impervious membranes 12 terminatingin an impervious membrane, and a lower header plate 16. The porous andbarrier membranes cooperate to form shallow channels of depths of theorder of the thickness of the porous membranes, through which theliquids comprising the evaporating and condensing layers are circulated.In the form of still shown, heat is transferred to lower header plate 16and transferred from upper header plate 14 so that in operation, thefeed liquid (e.g., salt water) is introduced between the underside ofeach porous membrane and the upper surface of the adjacent barriermembrane, and the product (e.g., potable water) is withdrawn from thechannels between the upper surfaces of the porous membranes and theadjacent barrier membranes. Any suitable means of a type well-known inthe art may be employed to transfer heat to and from the appropriateheader plates including, for example, employing the feed liquid, eitherdirectly or by a heat exchanger, to cool the upper header plate, andsolar energy, either directly of by a heat exchanger, to apply heat tothe opposite side of the stack of sheets.

impervious barrier membranes 12 are designed both to separate theevaporating and condensing liquid layers, to physically space apartporous membranes 10 to provide the channels containing the liquidscomprising the condensing and evaporating layers, and direct the flow ofthe liquids within the various layers thereof. Barrier membranes 12,shown in detail in FIG. 7, are preferably very thin having a thicknessof the order of .0010", and in order to support adjacent porousmembranes apart from one another to provide the requisite channels forthe liquids, the impervious barrier membranes are corrugated so as tohave a generally sinusoidal profile. In the embodiment of the stillillustrated in the drawings, and particularly in FIGS. 5 and 6, designedfor desalinating water, incorporating porous membranes 10 having athickness of approximately .0060" and designed to operate withevaporating and condensing layers of a thickness of the order of .0050",the corrugated barrier membrane may have a sinusoidal profile with acorrugation width, (i.e., wavelength) of approximately .0010 and acorrugation height (i.e., amplitude) of approximately .0070" prior toassembly in the still (see FIG. 7). When assembled as part of the still,the corrugated barrier membranes are compressed slightly as shown inFIG. 6, to provide adjacent, parallel channels on opposite sides of thebarrier membrane for conducting the liquids constituting the evaporatingand condensing layers.

Although gross heat transfer is from the bottom to the top of the stackof membranes in a direction generally perpendicular to the planes of themembranes, heat transfer [from] betwemz the product comprising acondensing layer contained in a channel designated 22, [to] and the feedliquid constituting the adjacent evaporating layer in a channel 24, isboth horizontal or parallel with the planes of the layers, as well asvertical or perpendicular to the planes of the layers. It will beapparent that the sinusoidal configuration of the barrier membranesoperates to increase the area of each barrier membrane in contact withadjacent condensing and evaporating layers so that heat transfer fromadjacent condensing and evaporating layers is improved. The corrugatedconfiguration of the barrier membranes provides a strong structure,highly resistant to compression for insuring that the passages [to],through which the liquids constituting the condensing and evaporatinglayers flow, remain open so that the liquids can flow freely in oppositedirections despite differences in the hydrostatic pressure of theliquids in adjacent layers. In the assembly of membranes comprising thestill, the corrugations and the channels provided thereby, extend fromend to end of the assembly in generally parallel relation so that flowof the liquids comprising the condensing and evaporating layers islengthwise of the assembly.

The still includes means for feeding a liquid such as salt water to theproper channels to provide the evaporating layers; withdrawing theproduct liquid, e.g., potable water, from the channels containing thecondensing layers; and withdrawing the effluent, e.g., concentrated saltwater, from the channels containing the evaporating layers. These samemeans also provide for sealing the assembly of stacked membranes toprevent leakage of the liquids and in the form shown comprise aplurality of rectangular gaskets 26, generally coextensive in size andshape with the porous and barrier membranes. Each gaskets 26 is in theform of a frame having relatively narrow lateral portions 28, andrelatively wide end portions 30. Gasket 26 is disposed between eachbarrier membrane and the adjacent porous membrane so that the order ofmembranes and gaskets in the assembly is a barrier membrane 12, gasket26, porous membrane 10, gasket 26, and barrier membrane 12. The assemblyof membranes and gaskets is clamped between the header plates so thatthe lateral and end portions of the gasket, and the end and lateralmarginal portions of the porous and barrier membranes are undercompression sufficient to block or obstruct the channels and preventescape of the liquids from between the membranes and gaskets at theedges thereof. The end portions of the porous and barrier membranes andgaskets are provided with holes 32, similar to and aligned with holes 18in the header plates for accommodating bolts 20.

In order to provide for introduction and withdrawal of the liquidsconstituting the evaporating and condensing layers, the end portions ofthe porous and barrier membranes, and end portions 30 of the gaskets 26,are formed With aligned circular holes 34, and header plate 14 isprovided with similar circular holes 36 also aligned with holes 34. Thecompressive pressure on the end portions of the membranes and gaskets issufiicient to flatten, at least partially, the corrugated barriermembranes and prevent leakage into or from the conduits, defined byholes 34 and 36, between the various membranes. To provide forintroduction of the appropriate liquid from a conduit defined by holes34 between the proper porous and barrier membranes, slots or channels 38are provided in end portions 30 of the gaskets extending from holes 34through the inner edge of the end portions of the gaskets. Thecorrugations of the barrier membranes extend into channels 38 where theyare engaged without being compressed between the end portions of thegaskets and the membranes and remain substantially in their extendedcondition (as shown in FIG. 5) Within the channels between adjacentporous membranes and gaskets to maintain the channels in an openposition on the appropriate sides of the barrier membranes. A suitableadhesive or sealant may be employed between the membranes and gaskets tofurther insure retention of the membranes together as a unitaryassembly, prevent leakage at the gaskets and fill the corrugations inone side of each barrier membrane in each channel 38. In the embodimentof the invention shown in FIG. 4. a flexible sealant or gasket materialsuch as a silicone rubber, may be applied as a continuous bead,designated 39 on each side of the end portion of each gasket in a zigzagpattern so as to form a flexible seal or gasket filling and blocking thecorrugations so as to isolate openings 34 on opposite sides of thegasket from the outer and inner edges of the end portion of the gasketand from openings 32 to confine the liquid to the conduits defined byopenings 34, except where it is intended that the liquid flow from theopenings through appropriate channels 38. In still another embodiment ofthe apparatus, the beads of flexible sealant material, i.e., siliconerubber, may be applied directly to the membranes in sufficient thicknessand arranged so as to perform the functions of the gaskets, namelyblocking or obstructing the channels formed by the corrugations andsealing the spaces between membranes at the lateral margins thereof,thus providing for a simple and inexpensive method of fabricating andassembling the structure. In other words, the beads of sealants wouldextend continuously throughout the end and lateral marginal portions ofthe membranes and around openings 34 therein except openings throughwhich liquids are intended to flow from condensing and evaporatingliquid channels 22 and 24.

The liquids are introduced into and withdrawn from the still throughsuitable means such as manifolds 40 and 42 mounted on header plate 14 atopposite ends thereof. In the preferred form of the still shown in thedrawings, the feed liquid or infiuent is introduced at one end thereof,the efiluent is drawn off at the opposite end, and the product liquid isextracted from the still at the same end as the feed liquid isintroduced so that flow of the feed and product liquids constituting theevaporating and condensing layers is in opposite directions.Accordingly, the end portions of the gaskets at the end of the still atwhich the feed liquid is introduced and the product liquid is withdrawn,are provided with slots or channels 38 extending from the inner edge ofthe end portion to every other hole 34, and the gaskets are arranged sothat the slots in every other gasket are aligned, i.e., the slots inadjacent gaskets are staggered. The feed liquid is introduced throughthe conduits formed by every second hole 34, and the product liquid iswithdrawn through the conduits, defined by alternate holes 34 locatedbetween holes through which the feed liquid is introduced. In thismanner, the liquid layers located on opposite sides of each barriermembrane comprise the different liquids constituting the evaporating andcondensing layer. At the opposite end of the assembly from which theefliuent is withdrawn, holes 34 and 36 are fewer in number since thequantity of effluent is less than the quantity of feed water, and onlythose holes 34 in the gaskets having slots 38 through which the feedwater is introduced, are provided with slots 38 for forming channelsthrough which the effluent is withdrawn.

The feed liquid or influent, e.g., salt water, is introduced throughmanifold 40; the product liquid, e.g., fresh water, is withdrawn throughmanifold 40; and the effluent e.g., concentrated salt water, iswithdrawn from manifold 42. Manifold 42 is quite simple comprising ablock bolted to header plate 14 in covering relation to holes 36 in oneend of the header plate, and having a longitudinal channel or recess 44opening toward the header plate and communicating with holes 36.Manifold 40 is a double manifold inasmuch as it must deliver differentliquids to and from alternate holes 36 at one end of the header plate14. Manifold 40 comprises a block having two longitudinal channels,designated 46 and 48, defined by outer side walls 50 and end walls 52and separated by a medial wall 54. The medial wall is designed to extendacross and in closing relation to [walls] holes 36 in the header plateand the side and media] walls are provided with holes 56 aligned withholes [32] 18 in the header plate for receiving bolts 20. Channels 46and 48 communicate with openings in an end of the manifold in turncoupled to suitable conduits desig nated 58 and 60, for deliveringliquids to and from the channels. Medial wall 54 is formed with aplurality of delivery recesses or passages [60] 62, each positioned foralignment with a hole 36 in the header plate and with adjacent deliverypassages [60] 62. Adjacent passages [60] 62 open in opposite directionsinto channels 46 and 48 so that every other delivery passage provides aconduit from one of channels 46 to 48 to the appropriate holes 36 in theheader plate when the manifold is secured to the header plate in properposition. An appropriately formed gasket may be provided between thefacing surfaces of the manifold and header plate to prevent leakage ofthe liquids therebetween.

FIG. 8 of the drawings illustrates the flow patterns of the distillateand distilland liquids through the still. It will be noted that thedistilland liquid is introduced into the still between the membranesthrough alternate conduits 64 formed by openings 36 in the membranes andgaskets and flows, as shown by the solid lines and arrows, toward theopposite end of the still from which it is withdrawn through alternateconduit 66 formed by openings 36 in the membranes. The distillate liquidflows through the channels provided by the corrugated membrane in adireaction opposite to the direction of flow of the distilland liquidthrough the channels provided in the membrane, as shown by the brokenlines and arrows in FIG. 8, and is withdrawn from the still throughalternate conduits designated 68 disposed between conduits 64. In thecopending US. application of Franklin A. Rodgers. Ser. No. 531,463.filed Mar. 3, 1966, a still is disclosed shown similar to that of thepresent invention in which manifold 42 is a double manifold similar tomanifold 40, and distillate liquid is reintroduced into the stillthrough conduits 70 formed by holes 36 located between conduits 66. Itwill be apparent from the flow diagram shown in FIG. 8 that thedistillate and distilland liquids, immediately upon introduction into orimmediately prior to withdrawal from channels between adjacentmembranes, are required to flow transversely of the [chanels] channelsformed by the corrugations. In other words, each liquid, upon enteringby way of conduit 64 or 70, is immediately distributed laterally so asto fill all of the channels, formed by the corrugations through whichthe liquid than flows toward the opposite end of the still where itagain flows laterally and is withdrawn through the appropriate conduits66 or 68. Although lengthwise flow of the distillate and distillandliquids through the channels formed by the corrugations is in oppositedirections, lateral flow of the liquids near the ends of the still is inthe same direction.

In order to promote the lateral flow of the liquids and faciliatedistribution and collection of the liquids at the opposite ends of thestill, portions 72 of the corrugated membranes immediately adjacentgaskets 26 are not corrugated and remain planar or flat, as shown inFIG. 9, or are embossed in the form of dimples, as shown in FIGS. and11. By virtue of this construction, lateral flow of the liquidstransversely to the direction of fiow through the channels provided bythe corrugations, is facilitated so as to appreciably reduce both theenergy required to circulate the liquids and the likelihood of formationof deposits of the solute and/or minerals contained in the distillandsolution. The uncorrugated areas of the impermeable membranes againstwhich there is parallel (i.e., in the same direction) flow of theliquids constitutes a relatively small area of the membranes near theends thereof, which area is of a size designed to conduct the quantityof liquid required to flow laterally from or towards the conduitsthrough which the liquids are introduced and withdrawn.

The dimples, designated 74, shown in FIGS. 10 and ll, function in thenature of channels extending in both directions providing for bothlateral and lengthwise flow of the liquid While serving to space theporous membranes apart from one another and prevent the channels forlateral liquid circulation from closing.

It will be apparent from the foregoing that the construction, inaccordance with the invention, of the still and the various membranescomprising the still is such that the membranes may be formed rapidlyand inexpensively by mass production methods and assembly of themembranes and gaskets to form the multiple effects still is equallysimple and easily accomplished. This construction provides for excellentheat transfer and liquid flow characteristics contributing to a highdegree of efiiciency.

Since certain changes may be made in the above apparatus withoutdeparting from the scope of the invention herein involved, it isintended that all matter contained in the above description shall beinterpreted illustrative and not in a limiting sense.

What is claimed is:

1. Distillation apparatus comprising. in combination:

a plurality of [flat] generally planar, porous, polymeric membraneshaving pores containing substantially only gas and being substantiallyimpermeable to a vaporizable liquid for passing substantially only gasesincluding the vapor of said vaporizable liquid;

a plurality of generally planar barrier membranes impermeable to saidliquid and vapor:

said porous and barrier membranes being arranged in alternating,face-to-face, stacked, contiguous relationship throughout the stack;

said barrier membranes being corrugated to provide channels between said[fiat] porous membranes for holding and circulating liquids, thecorrugations arranged in a single direction:

means for circulating a distilland through some of said channels incontact with the sides of said porous membranes facing in one directiontoward one side of the stack of said membranes;

means for [circulating] withdrawing a distillate [through] from othersof said channels in contact with the opposite sides of said porousmembranes facing the other side of said stack of membranes; and

[means at said one side of said stack of membranes for transferring heatthereto: and

means at said other side of said stack of membranes for transferringheat therefrom] means for establishing a thermal gradient across saidstack of membranes.

2. Distillation apparatus as defined in claim 1 including gasketsengaged between said porous membranes and said barrier membranesadjacent the margins of said membranes [and means for retaining saidgaskets and said margins of said membranes in compression] to preventflow of said liquid and vapor from between said membranes and saidgaskets.

3. Distillation apparatus as defined in claim 1 wherein [at least theend portions of] said membranes [are] in chute and portions disposed ingenerally parallel planes, said end portions include aligned openingscooperating to form conduits for a! least ne 0; said liquids extendingnormally to the planes of said membranes and said corrugations of saidbarrier membranes extend in generally parallel relation between said endportions.

4. Distillation apparatus as defined in claim 3 including gasket meansengaged between said end portions of adjacent porous and barriermembranes and wherein conduits are formed for two of said liquids;

said gasket means including openings aligned with said openings in saidend portions for preventing escape of said liquids from said conduitsbetween said membranes and selectively directing one of said liquidsfrom said conduits into said channels between appropriate pairs of saidmembranes; and

means for [circulating] introducing and withdrawing 9 said [first]distilland and [second] distillate liquids respectively throughalternate conduits at one end of said [apparatus] stack of membranes.

5. Distillation apparatus as defined in claim 4 wherein said gasketmeans block said channels provided by said corrugations in one side ofeach of said barrier membranes in the region of alternate openings toprevent flow of one of said liquids from said conduits, formed by saidalternate openings, in contact with said one side of each of saidbarrier [mernbarnes] membranes;

said gasket means block said channels provided by said corrugations onthe opposite side of each of said barrier membranes in the regions ofthe remaining openings to prevent flow of the other liquid therefrom incontact with said opposite side of said each barrier membrane; and

said corrugations remaining unblocked by said gasket means providingchannels between adjacent porous and barrier membranes communicatingwith said conduits for conducting said liquids therefrom betweenadjacent porous and barrier membranes.

6. Distillation apparatus as defined in claim 3 wherein said barriermembranes include transverse portions im mediately adjacent said endportions shaped to provide channels, extending transversely of saidcorrugations and communicating with said conduits and said channelsformed by said corrugations, for conducting said liquids 10 transverselyof said corrugations between said membranes.

7. Distillation apparatus as defined in claim 6 wherein said transverseportions of said barrier membranes are [generally planar] free ofcorrugations.

8. Distillation apparatus as defined in claim 6 wherein said transverseportions of said barrier membranes are dimpled.

References Cited The following references, cited by the Examiner, are ofrecord in the patented file of this patent or the original patent.

UNITED STATES PATENTS 2,386,826 10/1945 Wallach et al. 202-236X2,758,083 8/1956 Van Hock et al. 210-23 X 3,060,119 10/1962 Carpenter210-22 3,129,146 4/1964 Hassler 202-172X 3,240,683 3/1966 Rodgers202-173 3,340,186 9/1967 Weyl 203-11 X NORMAN YUDKOFF, Primary ExaminerD. EDWARDS, Assistant Examiner US. Cl. X.R.

